Liquid circulation time in internal-loop airlift reactors

An experimental study was performed on the liquid circulation time (t(C)) in an internal-loop airlift reactor when the external operating conditions such as the gas flow rate, diameter (D-D) and length (L-D)of the draft tube, and unaerated liquid height (H-0) from the upper end of the draft tube were varied. The findings revealed that t(C) could be broadly categorized into two different regions with respect to the linear gas velocity (u(GR)) in the riser. In one region, to was proportional to uGR raised to the power of -1/3 and L-D raised to the power of 1/2. In the other region, t(C) was constant and increased in proportion to L-D. The values of to in both regions were independent of H-0 under the experimental conditions employed. On the basis of the experimental findings, empirical equations predicting t(C) in the two regions are presented.